Prior Art Statement
The following patents and publications are representative of the most relevant prior art known to the Applicant at the time of filing the application:
______________________________________ U.S. Patents and Documents 2,216,135 October 1, 1940 E. T. Rainer 2,308,981 January 19, 1943 S. S. Kistler 2,860,960 November 18, 1958 J. R. Gregor 3,246,970 April 19, 1966 R. E. Zimmerman 3,524,286 April 18, 1970 L. C. Wohrer 4,263,016 April 21, 1981 R. Hirschberg et al Foreign Patent Documents 4,823,954 July, 1983 Japan 3,026,294 A1 February 18, 1982 Fed. Rep. of Germany ______________________________________
It is known that grinding aids of various types may be used to enhance the cutting efficiency of resin bonded abrasive grain in grinding wheels and coated abrasives. Various combinations of abrasive grain and active filler materials supported together in a resin bond have been suggested for improving the grinding action of abrasive products and certain combinations have been found to be especially useful for grinding and/or cutting ferrous materials.
Resin bonded grinding wheels, including combinations of alumina and other abrasives grains with finely divided fillers such as cryolite, pyrites or FeS.sub.2, KAlF.sub.4, K.sub.3 AlF.sub.6, K.sub.2 SO.sub.4, PbCl.sub.2, PbO, Sb.sub.2 S.sub.3, and mixtures of these materials, are well known and available today. Typical wheels making use of such abrasives and fillers are thin cut-off wheels such as may be used for cutting tubes, bars and other metal objects but other types of resin bonded wheels, such as snagging wheels, are made with abrasives and active fillers.
It has been found that certain combinations of fillers provide a superior grinding quality when used in mixtures. Thus, it has been established that mixtures of FeS.sub.2 and K.sub.2 SO.sub.4 produce a synergistic effect as compared with these same active fillers used alone or in other combinations together in a phenolic bonded cut-off wheel with alumina abrasive.
As pointed out above, fillers which are compounds containing fluorine, chlorine, sulfur, iron, and alkali metals in combinations, are known and widely used.
The Rainier patent discloses sodium chloride, potassium chloride, elemental sulfur, and other alkali metal halides as fillers or grinding aids. Specifically disclosed, in addition to sodium and potassium chlorides, are calcium chloride, calcium bromide, barium chloride, barium bromide, and strontium chloride.
Alkali metal and fluorine containing compounds and iron disulfide are taught by Kistler. Cryolite, sodium fluoroaluminate, is used to advantage in combination with ferrous sulfide, ferric sulfide, ferroferric sulfide or iron disulfide as grinding aids.
The Gregor reference, so far as is relevant to the present invention, suggests the use of sodium fluoroaluminate and iron oxide inter alia, as useful fillers or grinding aids for resinoid bonded grinding wheels.
Still another alkali metal-halogen containing grinding aid is disclosed by Zimmerman viz. potassium fluoroaluminate. The fluorine containing compound is used in conjunction with iron disulfide.
The Wohrer patent advocates the use of numerous fillers, the most relevant of which are sodium fluoroaluminate, sodium chloride, iron disulfide or pyrites as it is most commonly known, potassium sulfate and mixtures of these compounds.
A very effective substitute for the toxic lead and antimony containing fillers which have been used in the past in this country and which still are used in many other countries, is the series of alkali metal chloroferrates taught by the Hirschberg et al citation. These complex salts, according to Hirschberg et al, have the formula EQU A.sub.x Fe.sub.y ++Fe.sub.z +++Cl.sub.x+2y+3z
where A is an alkali metal ion or ammonium ion, x is a number from 1 to 10, y is a number from zero to 1, z is a number from zero to 1, and y and z cannot be zero at the same time. It is also taught that these compounds are preferably used in conjunction with a basic inorganic compound such as zinc oxide, potassium carbonate or sodium sulfide. Specific alkali metal chloroferrates suggested are KFeCl.sub.3, K.sub.2 FeCl.sub.4, Na.sub.2 FeCl.sub.4, and NaK.sub.3 FeCl.sub.6.
In the conventional manner, the Hirschberg et al fillers are incorporated in the bond, e.g. phenol-formaldehyde resin, of a grinding wheel. The substitution in the bond of the Hirschberg et al filler for the usual lead chloride or antimony chloride, does not result in a product with better cutting or grinding characteristics.
It is pointed out by Hirschberg et al in column 3, lines 33-35 that the alkali chloroferrate fillers can be used alone or admixed with other known fillers for grinding wheels.
The German Patent Publication No. 3,026,294 Al is a further variant on the Hirschberg invention; Hirschberg is also the inventor of the subject matter contained in this publication. The German reference discloses the partially fluorinated analogues of U.S. Pat. No. 4,263,016 having the generic formula EQU A.sub.x FeCl.sub.y F.sub.z
where A is an alkali metal or ammonium ion, x is a number from 1 to 10, y has a value of from 0.1 to 12.9 and the sum of y and z equals at least 3. The use of this material with other known grinding wheel fillers is suggested e.g. pyrites.
The Japanese application No. 4823954 discloses a phenolic resin bonded grinding wheel which incorporates an alkali metal fluoroferrate e.g.. potassium fluoroferrate, as a grinding aid or filler. The presence of the fluoroferrate in the grinding wheel produces a product superior to like products containing cryolite or pyrites.